Porcine Somatotropin
Overview Porcine somatotropin, or pST, is a single polypeptide hormone produced in the pituitary gland of pigs. It is about 190 amino acids in length and targets the growth of muscle, while inhibiting the growth of fat (1). Many farmers inject their pigs with an artificially made version of this hormone to make their meat more lean. As pigs grow, the brain signals the release of pST, which begins to build body muscle. Once they reach 100 pounds, the pig's pituitary gland stops producing the pST, allowing fat build up. At this point in their growth, farmers can inject their pigs with pST, which promotes the growth of muscle rather than fat (1). Overall, the use of porcine somatotropin has shown to increase pig growth rate by 10-20%, increase muscle growth by 50%, increase productive efficiency by 15-35%, and decrease body fat by 80% (2). Background In the 1930s, scientists discovered injecting animals with pituitary gland extracts increased the growth rate and produced leaner meat. By purifying the extracts, scientists were able to identify the hormone somatotropin. Although this discovery was groundbreaking, the only source of the porcine somatotropin was through slaughtered pigs, which was very expensive. In the early 1980s, scientists discovered an easy way to produce a greater amount of pST at a cheaper cost. They were able to identify which gene coded for the somatotropin, isolate it, and insert it into a bacterial plasmid, thus producing an artificial somatotropin (1). Method Escherichia coli is a microorganism normally found in the stomach of animals. It reproduces at a very quick rate, which allows scientists to use them for experimental purposes. To create porcine somatotropin, scientists insert the gene into a plasmid, which is then taken in by a competent E. coli ''cell. The somototropin gene is then transcribed and translated using bacterial DNA replication processes. Since the ''E. coli reproduces rapidly, a large amount of somatotropin can be produced overnight. Once the E. coli have reproduced, the protein can be isolated and purified by the addition of buffers, RNase, and centrifuging. The purified form can then be inserted into the pig (1). The process of creating artificial DNA and proteins by inserting a gene into a chromosome or plasmid is known as recombinant DNA technology (3). Pros and Cons of Protein Recombinant DNA Porcine somatotropin has been very effective in increasing the amount of lean meat harvested from pigs. It is a hormone that targets only specific cells, doesn't accumulate in the tissues, and is species specific. However, because proteins are made of amino acids, it can be easily degraded when ingested. This means that in order to be effective, the hormone would need to be injected rather than fed to pigs. This can make more work for the farmer, as the pigs require an injection each day for full results (2). Resources 1. Porcine Somatotropin (pST). ISU Biotechnology Program. 2. The Efficiancy, Safety and Benefits of Bovine Somatotropin and Porcine Somatotropin. American Council on Science and Health, pdf. 3. Protein Expression and Purification. Science Direct.